minor #16849 [Form] fix EntityType with multiple=true return type (MrYamous)

This PR was squashed before being merged into the 4.4 branch.

Discussion
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[Form] fix EntityType with multiple=true return type

Small fix for #16805 about return type in form with multiple option

I'm doing this on version 4.4 because it's the older maintained, but maybe we need to correct further?

Commits
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0ad2d2f [Form] fix EntityType with multiple=true return type

Author: javiereguiluz

reference/forms/types/entity.rst

@@ -236,7 +236,16 @@ These options inherit from the :doc:`ChoiceType </reference/forms/types/choice>`
 
 .. include:: /reference/forms/types/options/group_by.rst.inc
 
-.. include:: /reference/forms/types/options/multiple.rst.inc
+``multiple``
+~~~~~~~~~~~~
+
+**type**: ``boolean`` **default**: ``false``
+
+If true, the user will be able to select multiple options (as opposed
+to choosing just one option). Depending on the value of the ``expanded``
+option, this will render either a select tag or checkboxes if true and
+a select tag or radio buttons if false. The returned value will be a
+Doctrine's Array Collection.
 
 .. note::